Modulation is fundamental to electrical communications. There is a variety of different modulation techniques known in the art for embedding a signal in a carrier wave. For example, in amplitude modulation (AM), the signal is encoded by variations in the amplitude of the carrier wave. As another example, a genus of modulation techniques called "angle modulation," encodes the signal with variations in the instantaneous angle or timing of the carrier wave. Two common species of angle modulation are frequency modulation (FM), in which the instantaneous frequency of the carrier wave is varied, and phase modulation (PM), in which the instantaneous phase of the carrier wave is changed. Other well-known examples of angle modulation are frequency shift keying (FSK) and phase shift keying (PSK) commonly used for digital signals.
Consequently, modulated signals embodied in a carrier wave and transmitted to a receiver circuit must be demodulated or detected in order for the transmitted signal to be recovered. Although a considerable amount of effort has been expended in engineering demodulating circuits, many common conventional demodulation circuits nevertheless exhibit certain disadvantages.
Some conventional signal demodulation circuits are specifically designed to detect a particular kind of modulated signal. However, it is often difficult to realize design savings by reusing the design of the circuit to adapt to a different modulation scheme. A related drawback is that some conventional circuits are difficult to re-engineer to be more sensitive to changes in amplitude or in frequency.
Some conventional demodulation circuits are implemented with multiple, complex analog stages or employ large lumped analog components, such as inductors. Such circuits are difficult to manufacture on a monolithic semiconductor substrate and are therefore difficult to miniaturize.
Some conventional, digital demodulation circuits sample an incoming signal, convert the sampled signal into a digital format, and store the result in a random access memory (RAM) buffer. Other conventional digital demodulation circuits require microprocessor intervention to process the incoming signal. In both these approaches, the data rate of the incoming signal is limited.